This invention involves a new pharmaceutical vehicle for active substances in the form of an anhydrous gel, namely for substances which are sensitive to oxidation.
Many active substances which are sensitive to oxidation caused by oxygen in the air are used in the treatment of dermatological conditions. Specific examples of these active substances include but are not limited to anthralin (also called dithranol) and its derivatives idoxuridine, tretinoin, etc.
Among these substances, the compound anthralin is particularly active in the treatment of psoriasis, but disadvantageously, is very easily degraded by oxygen, subsequently forming dark-colored quinones or polymers which can stain the skin as well as clothing.
Various mixtures for processing and administering unstable or easily oxidized substances such as anthralin are already known. In connection therewith, Belgian Pat. No. 894,778 teaches the use of thickened mixtures comprising at least one fatty acid alkyl ester, wherein the fatty acid contains 12 to 18 carbon atoms and the alkyl group, with or without a branched chain, has 2 or 3 carbon atoms, and at least one thickening agent selected from the silica group with a particle size under 30 .mu.M and polyethylene powders whose volumetric mass is between 0.90 and 0.96 (g/cm.sup.3).
The mixtures involved in the above-mentioned Belgian patent, although enabling anthralin and its derivatives to be stabilized, are not conducive to adequate penetration by the anthralin, thus causing the anthralin to concentrate in the upper layers of the skin, when the mixture is applied thereto.
Furthermore, the mixtures must be of a sufficient viscosity to prevent the product from dripping onto healthy skin and potentially irritating it. Even is mixtures using silicas or polyethylene-type resins as thickeners are sufficiently viscous, they are difficult to eliminate, which constitutes another drawback in addition to the fact that such mixtures do not always penetrate sufficiently.